Does high-dose metformin cause lactic acidosis in type 2 diabetic patients after CABG surgery? A double blind randomized clinical trial

Metformin is a dimethyl biguanide oral anti-hyperglycemic agent. Lactic acidosis due to metformin is a fatal metabolic condition that limits its use in patients in poor clinical condition, consequently reducing the number of patients who benefit from this medication. In a double blind randomized clinical trial, we investigated 200 type 2 diabetic patients after coronary artery bypass surgery in the open heart ICU of the Mazandaran Heart Center, and randomly assigned them to equal intervention and control groups. The intervention group received regular insulin infusion along with 2 metformin 500 mg tablets every twelve hours, while the control group received only intravenous insulin with 2 placebo tablets every twelve hours. Lactate level, pH, base excess, blood glucose and serum creatinine were measured over five 12 h periods, with data averaged for each period. The primary outcome in this study was high lactate levels. Comparison between the 2 groups was made by independent Student’s t-test. To compare changes in multiple measures in each group and analysis of group interaction, a repeated measurement ANOVA test was used. There was no significant difference between the 2 groups regarding pH, base excess, or bicarbonate intake (P>0.05). No patient showed lactic acidosis in either group. Lactate levels were 23.0 vs 23.4 in the insulin-metformin and insulin only groups when the study was started, respectively. At the end of the study, those levels were 18.7 vs 18.9, respectively. In addition, the ANOVA repeated measurement test did not show a significant difference in terms of changes in the amount of lactate level between the 2 groups during the five measurement tests of the study period (P>0.05). High-dose metformin (1,000 mg twice daily with insulin) does not cause lactic acidosis in type 2 diabetic patients after coronary artery